Coin detection system



Nov. 19, 1935 H. HOVLAND 2,021,308

COIN DETECTION SYSTEM Filed Feb. 28, 1955 2 Sheets-Sheet l CO/N CONTROLC/RCU/T C ORD i C/RCU/T mvs/vrop H. HO HA ND ATTORNEY 1935. H. HbvLAND2,021,308

COIN DETECTION SYSTEM Filed Feb. 28, 1955 2 Sheets-Sheet 2 CORD C/RCU/TC O/N CONTROL C/PCU/T Patented Nov. 19, 1935 UNETED STATES PATENT OFFICECOIN DETECTION SYSTEM Application February 28, 1935, Serial No. 8,588

8 Claims.

This invention relates to telephone systems in which prepayment orregistration of a coin isnecessary to obtain a connection with anothersubscriber, and in some cases with the operator. This is customarilyaccomplished by the deposit of a coin (usually a nickel) in a box,having one or more coin slots, at the calling station, the box beingprovided with a polarized electromagnet having an armature adapted to betilted in either of two directions depending upon the direction of thecurrent passed through its coil. A coin deposited in such a box isarrested therein in such a manner as to close a connection to groundfrom one side of the line through the coils of the electromagnet whichin some systems operates the line relay at the central ofilce and.lights the line lamp.

The coin thus arrested within the box may be diverted either into areturn chute, if the call cannot be completed, or into a collect chuteleading to a coin drawer, if the connection is established, by theproper tilting of the before-mentioned armature which is controlled bythe exchange operator by the application to the line, by means of one orthe other of two keys, of direct current of the proper polarity.

The time of collecting the coin may vary in different localities. Insome. cases, such as at public pay stations, the collection is made ator just before the start of conversation and in other cases, due tolocal conditions, when the conversation is concluded. In all cases,however, the coin is returned to the subscriber at once if the desiredconnection cannot be established.

At the operators position, a coin pilot lamp is provided which is causedto light when either of the two coin keys is operated, provided a groundexists at the calling station, and remains lighted as long as the key isheld depressed. If

the coin box mechanism functions normally, the

operation of the coin box electromagnet will dispose of the coin andwhen the magnet armature returns to normal, upon the release of the coincontrol key, the ground will be removed from the line and a secondoperation of the key would m ineffective to operate the magnet or lightthe coin pilot lamp. If, however, for any reason a ground on the lineexists after the coin control key has been operated and released, whichmight be caused by failure of the mechanism to properly dispose of thecoin or to an artificial ground applied through accident or intent, theoperator would be unaware of this condition unless she made a test bythe simple expedient of operating the coin control key a second time,whereupon the coin pilot lamp would light as an indication that thefirst operation of the key had not cleared the line. If successiveoperations of the key caused the synchronous lighting of the coin pilotlamp, the line would be considered out of 6 order and should receiveattention at once. Tests of this character are occasionally made by theoperating force at some exchanges, but in busy coin box operatorspositions, they can only be made at infrequent intervals due to the 10extra time and. labor involved. Hence, a coin box may be in trouble andinefiective to collect the proper toll for considerable periods of timebefore the trouble is recognized and corrected. Posessing a knowledge ofthe foregoing characl5 teristics of present day prepayment systems,unscrupulous users of this kind of telephone service sometimes seek toavoidpayment of the initial charge by artificially grounding the lineindependent of the coin box by which method, under present conditions,they are enabled to obtain a local connection without proper payment.Such fraudulent methods may consist in the application of a permanentground to the proper line wire or in applying ground to the line until acertain stage of the call is reached after which the ground is removed.

object of the invention is to detect such fraudulent practices withoutnecessitating any special act on the part of the operator other thanobserving the pilot lamp.

A feature whereby the foregoing object is attained resides in meanswhich, after responding to an initial operation of either the collect orrefund key, will display a pilot signal before the operator and hold itdisplayed unless a ground was present on the line which was removed bythe application of coin control current thereby retiring the signalwhich would be the condition and functional operation attending thenormal and legitimate use of the coin box.

In other words, means is provided for automatically retiring thedisplayed pilot signal only when ground is present on the line when thecoin disposal current is applied and said ground disappears immediatelyfollowing such current application. Under all other conditions, thesignal will persist until manually retired.

The invention will be understood from the following description and readin connection with the accompanying drawings,

1 Fig. l of which represents a calling subscribers line equipped with acoin device of the well-known type, as shown in United States Patent toO. F. Forsberg 1,043,219, or 1,076,285 to W. F. Hosford, and a cordcircuit arranged in accordance with the present invention, whichrequires for its proper functioning that the operator hold the coindisposal key operated long enough to permit at least two impulses of thecoin disposal current to be applied to the line; and

Fig. 2 represents an arrangement similar in operation to Fig. i withthis difference that the coin disposal key need be operated onlymomentarily whereupon the coin test apparatus is locked in an operatedcondition and is released on y when a coin ground exists at the callingstatic-n, which is removed by application of the disposal current to theline, or when a release key is manually operated.

A description of the operation of the circuit of Fig. 1 will first begiven.

Let be assumed that a subscribers station A, desirous of obtaining aconnection with another suhscriber, B, for example, has gained theattention of the operator either by inserting a coin or" the properdenomination in the device CD in addition to removing the receiver fromthe switch-hook, or without the initial deposit of such a coin, hasgiven the number of the desired subscriber to the operator, and has beenconnected as desired.

If the system is one that requires the initial deposit of a coin by thecalling subscriber, no further act on the subscribers part is necessaryunless the charge for the desired connection is greater than the coindeposited, in which case the operator will return the deposited coin inthe manner hereinafter described and request the deposit of the properamount of the charge. If, however, the system is one in which thesubscriber may call the operator without depositing a coin but requiressuch a deposit before a conversational connection can be establishedwith the called subscriber, the calling subscriber must, after givingthe number of the called subscriber to the operator, deposit a coin,usually a nickel, in the coin device before the connection can becompleted.

Since this invention has only to do with disposal of the coin at thecalling subscribers station once it has been deposited, it will beassumed that th coin has been deposited and that the desired connectionto the called subscriber has been established.

The operator, after making the connection and observing that the calledsubscriber has answered, which is usually indicated by the darkening ofthe called supervisory lamp of the cord circuit in use, is instructed tocollect the coin, i. e., to press the coin collect key, which in normaloperation will cause the coin held in suspense at the calling station tobe dropped into the coin receptacle or drawer provided for the purpose.

When the operator presses the collect key C, relay l in the cord circuitoperates in an obvious circuit. The operation of relay I disconnects, atits innermost contacts, the normal talking battery from the answering orcalling subscribers end of the cord circuit and closes at its contact 2a circuit to operate relay 3 in the common or position coin controlcircuit. This circuit is traced from ground through the left-handcontacts of key C, contacts 2 of relay l, uppermost back contact ofrelay 4 to battery through the lower winding of relay 3. Relay 3 looksin a circuit traced from battery through its upper winding and upperinner contacts through the lower back contacts of both relays 4 and 5,through the lowermost contacts of relay 3 to ground through the upperback contacts of key 6.

Relay 3, operated, lights lamp l9 by connecting ground from the uppercontacts of key 6 through the lower outer contacts of relay 8 to lamp isand causes at least two pulses of coin collect current to be transmittedover the line in the following manner: If the metallic segment ofinterrupter l is not in contact with brush 24, relay 8 is operatedimmediately. The circuit for this function is traced from ground throughthe left-hand contacts of key C, contacts 2 of relay 5, lower innerfront contacts of relay 3, the winding of relay 8 to battery throughresistance 9. Had the metallic segment of interrupter i been in contactwith brush 2%, relay 8 would not have operated until the segment brokecontact with the brush since relay 8 would have had ground connected toboth its winding terminals. One of these ground paths has already beendescribed and the other is traced from ground through the segmentofinterrupter 7, brush it, the upper outer contacts of relay 3, upperinner back contacts of relay 8 to the winding of relay 8. The use or"this pick-up arrangement assures the transmission of a complete collectpulse.

The operation of relay 3 causes the operation of relay 5 when themetallic segment of interrupter 7 makes contact with brush 24. Thiscircuit is traced from ground through the metallic segment ofinterrupter 1, brush 24, the

- upper outer front contacts of relay 8 to battery through the windingof relay 5. Relay 5, operated connects positive coin battery to the tipand ring conductors of line L to collect the coin in the usual manner.This circuit is traced from positive battery it through current limitinglamp I i, the right hand contacts of coin collect key C, the right-handback contacts of coin return key R, upper contacts of relay 5, thewinding of relay E2 to the lower contacts of relay 8. From the lowercontacts of relay 8 the circuit is traced through two parallel paths,one from the middle lower contact of relay 8 through the lower, outercontacts of relay I, the ring springs of plug l3 and jack M, the ringconductor of line L, the primary winding of induction coil 5, switchhookcontacts i1, transmitter IE to ground through the windings of coindevice CD and coin' contacts E8, the other path from the lowermostcontact of relay 8, uppermost contacts of relay l, the tip springs ofplug l3 and jack M, the tip conductor of line L, conductor 25 to groundthrough the windings of coin device CD and coin contacts [8.

Under normal operation, both the coin device CD and relay i2 operate inthis circuit. The coin device drops the coin in the coin drawer butground is maintained connected until the circuit is opened and the coinmagnet armature returns to its normal position. The operation of relayl2 causes the operation of relay 4 by connecting ground to its upperwinding through its upper inner back contacts. Relay 4 locks throughboth its windings, the path through its upper winding being tracedthrough its upper inner front contacts and the lowermost contacts ofrelay 3 to ground through the upper contacts of key 5 and through itslower winding and upper outer front contacts, contacts 2 of relay I toground through the left-hand contacts of collect key C. Thelockingcircuit of relay 3 is transferred on the lower contacts of relay4 from ground through the contacts of key 6 to ground through thecontacts of relay I2 and relay 3 being of the slow-to-release type doesnot release during the momentary open circuit while the lower armatureof relay 4 is passing from its back to its 1 front contacts.

When the metallic segment of interrupter I breaks contact with brush 24,relay releases and opens the coin collect circuit through the winding ofrelay I2 to the coin device. Coin device CD releases, disconnectingground from the line and relay |2 releases, transferring the holdingground for relay 3 from the contacts of relay 2 to the lower backcontact of relay 5.

After an interval, the metallic segment of interrupter I again makescontact with brush 24 and relay 5 again operates and connects coinbattery to line L as before. This time, however, no ground is present atsubstation A and relay l2 does not operate. With relays 5 and 4 operatedand relay I2 non-operated, the locking circuit of relay 3 is opened andrelay 3 releases, extinguishing lamp l9 and releasing relay 8. Therelease of relay 8 opens the operating circuit of relay 5 releasing it.Relay 4 remains operated, however, in the circuit through its lowerwinding and upper inner front contacts to ground through the contacts ofcollect key C, previously described, until the operator noting thedarkened lamp releases key C which opens the circuit to relay 4releasing it and returning the coin control circuit to normal.

The operation of the circuit for the return of the coin is the same asthat for collecting the coin described above except that coin return keyR is operated instead of key C. The operation of key R through itsleft-hand contacts operates relays and 3 as before but in this casenegative battery 25 through current limiting lamp 25 and the right-handfront contacts of key R is connected to the line through the contacts ofrelays 5, 8, and and the winding of relay l2 and this battery causescoin device CD to return the coin in the usual manner. Relay 2 being aneutral relay functions on either polarity of battery.

If for any reason the ground is not present at substation A when thecoin collect or coin return key is operated, or if the ground is presentbut is not removed by the application of coin collect or coin returncurrent to the line, lamp I9 remains lighted indicating that thesubstation apparatus has not functioned properly or has been tamperedwith. To illustrate this condition, let it be assumed that a ground isconnected with fradulent intent, or otherwise, to conductor 20. Theoperation of the circuit is the same as described above until the secondpulse of coin collect battery is transmitted over the line. In thiscase, relay I2 operates on the second pulse since the ground is notremoved by the operation of the coin device.

"The operation of relay l2 provides a holding path for relay 3 duringthe time relay 5 is operated, thus causing relay 3 to remain operated.This circuit is traced from ground through the contacts of relay I2,through the lower front contacts of relay 4 to battery through the upperinner contacts and upper winding of relay 3. Lamp I9 remains lighted asan indication of trouble and the coin control circuit transmits pulsesof coin collect current over the line until the operator releases thecollect key C. In order to release the coin control circuit andextinguish lamp I9, it is necessary tooperate key 6 which operation willbe described later.

Had no ground been present on the line when coin collect key C wasoperated, relay |2 would not have operated on the first pulse andconsequently relay 4 would have remained in a released condition. Withrelay 4 released, relay 3 remains operated under control of key 6. Thecircuit for holding relay 3 operated is traced from ground 5 through theupper back contacts of key 6, lowermost front contacts of relay 3, lowerback contacts of relay 4 to battery through the upper inner contacts andupper winding of relay 3. With relay 3 operated, lamp l9 remeans lightedas in 10 the case of a ground on line L.

In order to release the coin control circuit when the coin device hasnot functioned normally, it is necessary to operate release key 6. Theoperation of this key opens the locking circuits of relays 3 and 4releasing them and extinguishing lamp I9. The operation of key 6 alsocauses the operation of relay 2| through the left-hand back contacts ufthe latter. Relay 2| locks through its left-hand front contacts fromground through the contacts of key 23 and lights lamp 22 through theright-hand contacts of relay 2| as an indication of failure. After thetrouble has been recorded or cleared, key 23 is operated which releasesrelay 2| and extinguishes lamp 22. 25

Referring now to Fig. 2, a circuit is shown which accomplishes the sameresult as Fig. 1, except that only a momentary operation of the coincollect or coin return keys is required. As in the caseof Fig. 1, it isassumed that a connection V has been established between subscriber CSand another subscriber in the exchange AS, and that it is desired toeither collect or return the coin by applying positive or negative coinbattery to the line. 35.

To collect the coin at the subscribers station, the operator depresseskey II, which causes the operation of relay 53 by connecting ground toits lower winding terminal. With relay 53 operated, ground through thecontacts of key 1| is 40 connected through contacts 80 of relay 53, theupper middle back contacts of relay 63, the upper outer back contacts ofrelay 6| to battery through the lower winding of relay 54. Relay 54operates in this circuit and looks over a circuit traced from batterythrough its upper winding and upper inner contacts through the upperouter back contacts of relay 59 and the lower inner back contacts ofrelay 6| in parallel to ground through -the lower outer front contactsof relay 54 and the upper back contacts of key 64. Relay 54 operated:Lights lamp 65 by connecting ground through the upper back contact ofkey 64 and the lowermost front contacts of relay 54 to battery throughthe filament of lamp 65; holds relay 5355 Y operated in a circuit tracedfrom ground through the upper contacts of key 64, lower middle frontcontacts of relay 54, contacts flll and lower winding of relay 53 tobattery; and starts the coin control circuit in operation to send atleast two pulses of coin battery over the line in the following manner:

Relay 55 operates immediately after relay 54 closes its contactsprovided the metallic segment of interrupter 56 is not in contact withbrush 51. Relay 55 is provided as a pick-up device to prevent sendingout a short pulse should relay 54 operate during the time that themetallic segment of interrupter 56 is connected to brush 51. Should thisoccur, ground is connected to both winding terminals of relay 55 toprevent its operation. Thus ground through the upper back contacts ofkey 64 through the lower middle front contacts of relay 54 is connectedto the rightthrough the metallic segment of interrupter 56, brush 51,the upper outer front contact of relay 54 and the upper inner backcontact of relay 55 is connected to the left-hand winding terminal ofrelay 55. When the metallic segment of interrupter 56 breaks contactwith brush 51, or if it was not in contact with brush 5'! at the timerelay 54 operated, relay 55 operates in a path traced from groundthrough the upper back contacts of key 64, lower middle front contactsof relay 54, the winding of relay 55 to battery through resistance 58.

Relay 55, operated, connects interrupter 56 to interrupter relay 59 andrelay 59 operates each.

time the metallic segment of the interrupter makes contact with thebrush as long as relay 55 remains operated. This circuit is traced fromground through the metallic segment of interrupter 56, brush 51, theupper outer contacts of relay 55 to battery through the winding of relay59. When interrupter relay 59 operates under control of interrupter 56 apulse of positive coin collect battery is transmitted over line 5!] tooperate coin device 5!. This circuit is traced from positive battery 66through current limiting lamp 61, lower back contacts of relay 62, lowerinner front contacts of relay 59, the winding of relay 69 to the lowerinner front contacts of relay 55. From the lower inner front contacts ofrelay 55, the circuit divides so that the coin batfront contacts ofrelay 53, the tip springs of plug T8 and jack l1, tip line wire of line55, conductor Hi, to ground through the windings of coin device 5| andcoin contacts 52. The circuit over the ring wire is traced from contact8! of relay 55, lower outer contacts of relay 53, the ring springs ofplug 18 and jack the ring conductor of line 50, the winding of inductioncoil 15, switch-hook contacts 82, transmitter 16, conductor 14, toground through the windings of coin device 5! and coin contacts 52. Coindevice 5! and relay 69 both operate in this circuit. The coin devicedisposes of the coin but ground is maintained connected to the deviceuntil the circuit is opened and. thecoin magnet armature returns tonormal. The operation of relay 55 causes the operation of relay 6! in acircuit traced from ground through the contacts of relay 65, theuppermost back contacts of relay 63, to battery through the upper innerback contacts and upper winding of relay 6!. Relay 6! is of the slowoperate type to prevent its false operation when the lower outercontacts of relay 59 are connected together while the latter relay isoperating and releasing. Relay 6! locks through both its windings. Thelocking circuit for its upper winding is traced from ground through theupper back contacts of key 64, lower outer front contacts of relay 54,to battery through the upper inner front contacts and upper winding ofrelay 5!. The locking circuit for the lower winding of relay 5! istraced from ground through the upper back contacts of key 64, lowermiddle front contacts of relay 54, upper middle back contacts of relay63, to battery through the upper outer front contacts and lower windingof relay 6i. With relays 59 and 5! both operated, the locking path forrelay 55, described previously, is opened but ground through thecontacts of relay 65, through the uppermost back contacts of relay 63and the lower inner front contacts of relay 6! holds relay 5 lockeduntil relay 59 releases and closes the locking path first described.

When relay 59 releases under control of interrupter 56, the coin collectcurrent is removed from the line, releasing relay 65, and coin device 5!which disconnects the ground from the line. With relay 5! operated andrelay 59 released, a circuit is closed for the operation of relay 63.This circuit is traced from ground through the upper back contacts ofkey 55, lower outer front contacts of relay 54, upper inner frontcontacts of relay 6!, upper inner back contacts of relay 59 to batterythrough the upper winding of relay 63. Relay 63 locks in a circuittraced from ground through the upper back contacts of key 64, lower 157outer front contacts of relay 54, upper inner front contacts of relay 6tobattery through the upper inner front contacts and upper winding ofrelay 63.

When interrupter 55 again operates relay 59 20';

coin collect battery is again applied to both conductors of the lineover paths already traced. In this case, however, ground is not presentat coin contacts 52, and relay 6% does not operate.

With relays 59 and 6! both operated and relay 6% released, the lockingpath for relay 5! is opened and relay 54 releases. The release of relay54 releases all of the relays in the circuit and extinguishes lamp 65.

The operation of the circuit for the return of 7 the coin is the same asthat described above for the collection of the coin except that key "illis depressed instead of key I! and relay 62 is operated and locked whichconnects negative battery 68 to the line instead of positive batterywhen ll 'Z,

relay 59 operates. The circuit for the operation of relay 62 is tracedfrom ground through the left-hand contacts of key 10, to battery throughthe lower winding of relay 62. Relay 62, operated,

locks in a circuit traced from ground through the 40 upper contacts ofkey 64, lower middle contacts of relay 54 to'battery through the uppercontacts and upper winding of relay 62. With relay 62 operated, the coincurrent path is traced from negative coin battery 68, through currentlimiting lamp 69, lower front contacts of relay 52 to the lower innerfront contacts of relay 59. The circuit from this point is the same aspreviously traced for the coin collect function. Relay 62 is releasedupon the release of relay 54 as previously described.

Had no ground been present on the line or if a ground was present butwas not removed by the operation of the coin device, the circuit isarranged to remain locked in and. lamp 65 to 55 operates on the secondpulse as well as the 65 first since ground is not removed by theoperation of the coin device. Relay 54 releases, releasing relays 55,65, El, and 52 as before but relay 54 being somewhat slow in releasingallows the operation of relay 66 to hold relay 53, which 70 is also slowto release, operated until the locln ng path of relay 63 is taken up byrelay 59. The circuit for holding relay 53 operated frorn'the contactsof relay 59 is traced from ground through the contacts of relay 6!),contacts 83 of When coin collect 60 relay 59 to battery through thelower inner contacts and lower winding of relay 63. After relay 59releases, this locking circuit is modified so that ground through theupper contacts of key 64, through the lowermost back contacts of relay59 holds relay i3 operated through its lower inner front contacts andlower winding.

By this method of operation, thedesirable feature of applying but twopulses of coin current to the-line is obtained and the subsequentremoval of the ground does not satisfy the circuit as it does in thecase of the circuit shown in Fig. 1. Relay 63 remains locked operatedand holds lamp B5 lighted until the operator, noting the lighted lamp,records the line number and operates release key 64. The operation ofthis key opens the locking circuit of relay t3 releasing it andextinguishing lamp 65. The operation of key 64 also causes the operationof relay it in a circuit traced from ground through the lower contactsof key fi l to battery through the lefthand back contacts and winding ofrelay 12. Relay 12, operated, locks through its left-hand front contactsto ground through the contacts of key 19 and lights lamp T3 at asupervisory position. The supervisor may release relay l2 and extinguishlamp I3 by operating key l9.

If no ground had been present on the line when key Ill or H wasoperated, relay would not have operated on the first pulse and relay 6!would have remained in a released condition. With relay 6| released,relay 54 is held operated over paths already described and the circuitcontinues to transmit pulses of coin battery over the line and lamp 65remains lighted until the operator noting the lighted lamp releases thecircuit by operating release key 64 as previously described.

What is claimed is:

1. In a prepayment coin system, a subscribers station, a central ofiice,a line therebetween, a coin device at the station connected to the lineand adapted to receive a coin and hold it in suspense thereby applying aground condition to the line through said device, said device beingfurther adapted to be actuated by current of a predetermined voltagereceived over the line and flowing to said coin ground to dispose of thecoin thereby removing the said ground condition, a pilot signal at thecentral oflice, a grounded source of intermittent current impulses atthe central ofiice of such predetermined voltage as to actuate said coindevice, operator-controlled means adapted to initiate the connection ofsaid intermittent current source to the line and to display said pilotsignal, and other means automatically responsive thereafter to retiresaid displayed signal and disconnect said source from the line when apredetermined current flows through the line upon the application of oneimpulse and no current flows upon the next succeeding application,thereby indicating that the coin device has functioned in a normalmanner.

2. In a prepayment coin system, a subscribers station, a central ofiice,a line therebetween, a coin device at the station connected to the lineand adapted to receive a coin and hold it in suspense thereby applying aground condition to the line through said device, said device beingfurther adapted to be actuated by current of a predetermined voltagereceived over the line and flowing to said coin ground to dispose of thecoin thereby removing the said ground condition, a pilot signal at thecentral o-flice, a grounded source of intermittent current impulses atthe central office of such predetermined voltage as to actuate said coindevice, operator-controlled means adapted to initiate the connection ofsaid intermittent current source to the line and to display said pilotsignal, and other means automatically responsive thereafter to maintainsaid signal displayed as long as successive current impulsesencounterthe same line condition either grounded or ungrounded.

3. In a prepaymentcoin system for telephone exchanges in which groundingthe line at a subscribers station by means of a deposited coin isnecessary to obtain a connection with another line at the central ofliceand in which the coin is collected or returned to the subscriber bymeans of current of a predetermined voltage transmitted over the lineunder control of the operator, automatic means initiated by the operatorfor periodically transmitting current impulses over the line to disposeof the deposited coin thereby removing said ground, and means includinga signal adapted to be displayed upon initiation of said automatic meansand main tained displayed as long as the current impulses transmitted tothe line encounter the same line condition, either ground or absence ofground.

4. In a prepayment coin system for telephone exchanges in whichgrounding the line at a subscribers station by means of a deposited coinis necessary to obtain a connection with another line at the centraloffice and in which the coin is collected or returned to the subscriberby means of current of a predetermined voltage transmitted over the lineunder control of the operator, auto" matic means initiated by theoperator forperiodically transmitting current impulses over the line todispose of the deposited coin thereby removing said ground, and meansincluding a sig nal adapted to be displayed upon initiation of saidautomatic means and retired if the first current impulse transmittedencounters a ground on the line and no ground is encountered upon thetransmission of the second impulse.

5. In a prepayment coin system for telephone exchanges in whichgrounding the line at a subscribers station by means of a deposited coinis necessary to obtain a connection with another line at the centraloffice and in which the coin is collected or returned to the subscriberby means of current of a predetermined voltage transmitted over the lineunder control of the operator, automatic means initiated by the operatorfor periodically transmitting current impulses over the line to disposeof the deposited coin thereby removing said ground, and means includinga signal adapted to be displayed which is locked in and remainsdisplayed until manually released by the operator if the first impulsetransmitted to the line does not encounter a ground condition thereon.

6. In a prepayment coin system for telephone exchanges in whichgrounding the line at a subscribers station by means of a deposited coinis necessary to obtain a connection with another line at the centraloffice and in which the coin is collected or returned to the subscriberby means of current of a predetermined voltage transmitted over the lineunder control of the operator, automatic means initiated by the operatorfor periodically transmitting current impulses over the line to disposeof the deposited coin thereby removing said ground, means including asignal which is displayed responsive to the initiation of said automaticmeans, and means for retiring the displayed signal only when ground ispresent on the line at the time the first impulse of current istransmitted,

which ground disappears immediately following such current impulse andbefore the second impulse is transmitted.

7. In a prepayment coin system for telephone exchanges in whichgrounding the line at a subscribers station by means of a deposited coinis necessary to obtain a connection with another line at the centraloflice and in which the coin is collected or returned to the subscriberby means of current of a predetermined voltage transmitted over the lineunder control of the operator, automatic means initiated by the operatorfor periodically transmitting current impulses over the line to disposeof the deposited coin thereby removing said ground, means including asignal which is displayed responsive to initiation of said automaticmeans, and means for retiring the displayed signal only when ground ispresent on the line when one impulse of current is transmitted and isnot present when the next succeeding impulse is transmitted.

8. In a prepayment coin system for telephone exchanges in whichgrounding the line at a subscribers station by means of a deposited coinis necessary to obtain a connection with another line at the centralofiice and in which the coin is disposed of by means of current of apredetermined voltage transmitted over the line under control of theoperator, automatic means initiated by the operator for periodicallytransmitting current impulses over the line to dispose of the depositedcoin thereby removing said ground, means including a signal which isdisplayed responsive to initiation or said automatic means, and meansfor retiring the displayed signal only when one impulse of currentencounters ground on the line and the next succeeding impulse encountersno ground.

HENRY HOVLAND.

